Nuclear fusion, the powerful reaction that powers the Sun, also has the potential to provide abundant clean energy on Earth.
For instance, the amount of energy produced by burning 2,400 gallons of oil or several million tons of coal can be generated by the fusion of just one gram of deuterium-tritium (a type of nuclear fusion fuel), and that too without releasing any greenhouse gases.
This is why scientists in many parts of the world are trying to make fusion reactions practical and scalable. However, it's not as easy as it sounds. For a fusion reaction, plasma is required to be heated to hundreds of millions of degrees Celsius -- this is seven to eight times more than the temperature found at the Sun's core.
At first, it may seem impossible to heat plasma to such extreme temperatures, but a new study from researchers at the Princeton Plasma Physics Laboratory (PPPL) suggests that it can be achieved using a Faraday screen.
One of the methods that scientists use to heat plasma is called wave heating or radio frequency (RF) heating. This approach involves using electromagnetic waves to shoot up the temperature of the plasma.
When high-frequency waves are injected into the system, they transfer their energy to the charged particle inside the plasma, which causes them to move faster and collide more frequently, leading to a sharp increase in the plasma temperature.
This is similar to how microwaves in an oven interact with water molecules in food. These waves transfer energy to the molecules, causing them to vibrate rapidly. This vibration generates heat, which raises the temperature of the food.
However, this approach has a limitation that prevents the plasma from achieving the required temperature. RF heating also results in additional waves other than the ones that heat the plasma.
These extra waves, called slow modes, lead to energy losses and end up reducing the overall plasma temperature. The study authors ran some simulations that revealed a technique capable of overcoming the slow modes.
"We have performed computer simulations confirming a technique that prevents the production of the unhelpful waves, known as slow modes, boosting the heat put into the plasma and increasing the efficiency of the fusion reactions," the PPPL team notes.
For the first time, the PPPL team ran some 2D simulations to figure out a way of reducing slow modes. During their study, they discovered that when Faraday screens (also called the Faraday cage) are placed at five-degree angles to the antenna that generates electromagnetic waves to heat plasma, slow modes are not produced.
Faraday screen which is made of conducting material, like metal works as a protective barrier blocking or reducing electromagnetic waves.
The simulations demonstrated that the screen allowed the low-frequency heating waves (called the helicon waves) from the antenna to pass into the plasma. However, slow modes were stopped.
"The simulations confirmed suggestions made by previous researchers indicating that when the Faraday screen was aligned at an angle of five degrees or less from the orientation of the antenna, the screen, in effect, short-circuits the slow modes, making them fizzle out before they propagate into the plasma," the study authors said.
However, as the screen angle was further increased, the slow mode frequency also rose sharply. This observation suggests that plasma temperature is super sensitive to the orientation of the Faraday screen.
The researchers now plan to explore other ways to limit slow modes. These efforts will make it easier to achieve the required ultra-high temperatures needed for fusion reactions.